Mechanical couplers such as clutches are used in a wide variety of applications to selectively connect and disconnect a driving mechanism to and from a driven mechanism. Typical uses include automotive applications such as vehicular transmissions and self-propelled applications such as riding or walk-behind lawn mowers and other mobile powered equipment. The driving mechanism supplies input power and the driven mechanism receives the input power to provide an output response. When a clutch is positioned in a coupled state, its associated driving mechanism is mechanically referenced to the corresponding driven mechanism so that the power supplied by the driving mechanism is transmitted to the driven mechanism. For example, the driving mechanism can constitute or be connected to the output shaft of a motor, and the driven mechanism can constitute a wheel, a cam mechanism, or some other component that rotates or reciprocates. In one common clutch design, the coupling between the driving and driven mechanisms is accomplished by way of friction. For example, a spinning plate connected to a power input can be brought into frictional contact with another plate to cause the other plate to spin. In another common design, the coupling is accomplished by way of a pawl, dog, tooth, pin or catch that brings the driving mechanism into positive engagement with the driven mechanism. Coupling apparatus are examples of this latter design.
As known to persons skilled in the art, a self-propelled lawnmower is designed to utilize the rotational power developed by its motor both for powering its cutting blades and for selectively powering one or more of its wheels through a suitable transmission assembly. Accordingly, self-propelled lawnmowers often include one or more types of clutches. Most self-propelled lawnmowers utilize an on/off clutch of varying design inside the transmission assembly, as well as a 1-way ratchet disposed at the wheel area external to the transmission assembly. The operator of the lawnmower utilizes a cable to engage and disengage the internal transmission clutch and thus control whether or not power from the motor is transmitted to the wheel or wheels. When disengaged, the internal transmission clutch allows the lawnmower to be rolled backward. Due to the design of the internal transmission clutch, the 1-way ratchet is needed between the output of the transmission assembly and the wheels to enable the lawnmower to be rolled forward when the motor power is de-coupled from the wheels. Typically, an additional cable is utilized to control driving speed.
In some recent lawnmower designs, a conventional internal transmission clutch is not needed. For example, on/off drive control can be implemented by employing a belt to disengage a clutch, and speed is controlled by a variable-pitch pulley. In such a case, one cable can be used both for controlling the clutch and for varying the driving speed. While in this case the internal transmission clutch is not needed, it nonetheless would be desirable to provide a means for enabling the lawnmower to be rolled forward and backward when power from the motor is not being transmitted to the wheels. It would therefore be advantageous to provide a 2-way or bi-directional clutch that not only selectively transmits power from a driving mechanism to a driven mechanism, but also permits the driven mechanism, such as wheels for example, to be freely rotated in both the forward and reverse directions when the clutch is disengaged.
A clutch that permits freewheeling in both directions when disengaged is disclosed in U.S. Pat. No. 4,909,365 to Tillotson et al. The driving member of this clutch is an output shaft in which a keyway is formed. The output shaft is supported through the aperture of a housing. The driven member of the clutch is a pinion gear that is supported on the output shaft and includes several keyways spaced at 1 EH-degree intervals. In addition, a friction disk is supported on the output shaft and is located between the pinion gear and a wall of the housing. A key is supported both by the keyway of the output shaft and by a relief formed in the friction disk. An axially oriented thrust spring biases the pinion gear into contact with the friction disk, and thus pushes the friction disk against the housing. To engage the clutch, the output shaft is rotated. This rotation of the output shaft causes the key to rotate around the shaft and the friction disk to bear on the key. Once the keyway of the output shaft becomes aligned with one of the keyways of the pinion gear, the friction disk forces a portion of the key into the keyway of the pinion gear, thereby driving the pinion gear. As described in the patent, the frictional load produced by friction disk is needed to engage the clutch.
Another clutch that permits bi-directional freewheeling is disclosed in U.S. Pat. No. 5,307,911 to Robinson. This clutch consists of a central drive shaft, a concentrically disposed output shaft, and an annular clutch assembly between the drive shaft and the output shaft. In addition, the drive shaft is coaxially disposed about a fixed stub shaft. A portion of the drive shaft is octagon-shaped, with its outer surface consisting of eight flat chord sections. The clutch assembly consists of an annular ring of eight roller bearings joined together by a cage. Each roller bearing is positioned on one of the chord sections of the drive shaft. An annular friction band is coaxially disposed about the stub shaft. The friction band is disposed between the stub shaft and the cage of the roller bearings, and contacts both the stub shaft and the cage. As the drive shaft rotates, each roller bearing moves into an extreme position between its corresponding chord section and the inside surface of the output shaft. The friction band is needed in order to impart friction to the roller bearings so as to hold the roller bearings in their respective extreme positions. As a result, the drive shaft drives the output shaft. In order to stabilize this clutch, four distinct sets of bearings are required in addition to the bearings disposed on the chord sections.
Clutches of the type disclosed in U.S. Pat. Nos. 4,909,365 and 5,307,911 in which engagement requires the development of friction use several components that, in operation, are subjected to large amounts of heat energy and impact, and hence are prone to wearing, loss of material, and failure. It would therefore be advantageous to provide a 2-way or bi-directional clutch that does not rely on frictional contact for engagement, and thus is less prone to premature wear and failure in comparison with previous clutch designs.